This study will attempt to clarify the role of the intrarenal release of prostaglandin E2 (PGE2) inthe maintenance of sodium balance in normal and pathologic states. A substantial body of information has accumulated from this and other laboratories which suggests that the intrarenal release of PGE2 may be associated with the way in which the kidney is able to handly both fluids and electrolytes. To further investigate the physiologic role of renal PGE2, experiments will be designed to approach the problem in several ways. With the use of an extremely sensiive and specific protein receptor assay, renal excretory rates of PGE2 will be masured in numerous experimental models of alterations in sdium excretion including diuretic administration, use of vasoactive drugs and hormones, and with various states of sodium balance. Other studies will be performed in animals with various models of either salt-retaining or salt-wasting states. Finally the various interrelationships between PGE2 and vasopressin release will be investigated in chronically instrumented conscious dogs in various states of water balance and endogenous vasopressin release.